Resolving the sign ambiguity in Delta Gamma_s with B_s -> D_s K

TL;DR

This paper proposes a method to resolve the sign ambiguity in the width difference of B_s mesons by using B_s -> D_s K decays, enhancing the precision of CP phase measurements.

Contribution

It introduces a strategy to eliminate the sign ambiguity in Delta Gamma_s using B_s -> D_s K decays, improving upon existing analysis methods.

Findings

Tagged analysis is more promising than untagged.

Sign ambiguity can be resolved with low statistics.

Method is suitable for early-stage B_s -> D_s K studies.

Abstract

The analysis of tagged B_s -> J/psi phi decays determines the CP phase phi_s in B_s-anti-B_s mixing with a two-fold ambiguity. The solutions differ in the sign of cos(phi_s) which equals the sign of the width difference Delta Gamma_s among the two B_s mass eigenstates. We point out that this ambiguity can be removed with the help of B_s -> D_s K decays. We compare untagged and tagged strategies and find the tagged analysis more promising. The removal of the sign ambiguity in Delta Gamma_s can be done with relatively low statistics and could therefore be a target for the early stage of B_s -> D_s K studies.